1. Field of the Invention
The present invention relates to a wrist mechanism in an industrial robot, which is used, for example, to treat work piece materials for machine tools.
2. Description of the Prior Art
In one prior art device, a wrist mechanism in an industrial robot has been used in which the angular positioning for any desired position is carried out with a servo control device. However, the servo control device is very expensive; thus the servo control device has not been widely used in this field.
In another prior art device, a wrist mechanism in an industrial robot has been used in which the angular positioning is carried out with the angular positioning device for two positions. The device, for example, comprises a rotary type actuator having two air intakes. The rotor of the rotary type actuator rotates clockwise when the air pressure is applied to one of the air intakes and the rotor rotates counterclockwise when the air pressure is applied to the other air intake. A pawl is provided coaxially with the rotor of the rotary type actuator and stops the rotor at desired angular positions cooperating with stoppers, which are located on the outer portion of the stator of the rotary type actuator, so that the angular positioning of the wrist mechanism of an industrial robot, which is linked with the rotor of the rotary type actuator, is carried out. An angle between two stopping positions of the wrist mechanism is decided by the relation of the shape of the pawl and the positions of the stoppers.
In recent years, the necessity of various positions, for example, positions of angles of 0 degree, 90 degrees, 180 degrees and 270 degrees from the reference position, is required frequently because of applications in which the wrist mechanism has double grasping portions, the necessity of working both a front surface and a back surface, and the relations of the locations between the work and the work locating base or the work transferring device. For the above mentioned four positions, hitherto a wrist mechanism using the conventional servo controlled positioning was utilized, or two angular positioning devices for two positions was utilized, putting the devices one upon another. For these reasons, problems exist in the conventional wrist mechanisms, in that the cost of the wrist mechanism becomes very expensive and the wrist mechanism is not practical, because of the large size of the mechanism compared with the functions thereof. The wrist mechanism using the angular positioning device for two positions comprising the rotary type actuator was disclosed in U.S. Pat. No. 4,274,802, issued June 23, 1981, by the inventor of the present invention.
The present invention is proposed to solve the above mentioned problems in conventional wrist mechanisms.